Remote zones have been monitored for security purposes in the past by placing sensors at the zones and having communication lines extending from the sensors to a central control location. Changes in the operating conditions of the sensors can be detected by the actuation of visual or sound indicators at the central control location. However, systems of conventional design for carrying out these purposes have been complex in construction and costly to manufacture and operate. For this reason, a need has arisen for improvements in monitoring systems for a plurality of remote zones which give information about status changes of remote zones and permit the monitoring of the zones without requiring special skills and without the need for complex circuitry.